Life from conception to old age and death includes prenatal, infant, toddler, preschooler, child, adolescent, adult and older adult stages. These stages or similar classifications prove useful to understand the human experience from various perspectives through studies of physical growth and development, nutritional science, psychosocial development and cognitive development across the lifespan.
Stages
Loosely bounded on either end by a transition and defined by the major challenges faced, life cycles represent a time of specific developmental accomplishments. For instance, the prenatal period is physically bounded by conception on one end and birth on the other and includes the dramatic physical changes that culminate in the ability to sustain life outside the womb.
Physical
Physical life cycles mark transitions from a single cell to dynamic growth as an infant in the first year and mastery of gross and fine motor skills as a toddler with increased independence and exploration of the environment and new language skills as a preschooler.
During the school-age years, children grow in spurts but slower than they did in infancy and than they will again in adolescence, the time of profound biological changes through which a child develops into an adult. By early adulthood, body composition shifts with hormonal changes and continues to shift through late adulthood with loss of physical resilience and declining function.
Nutritional
Age-appropriate nutrition remains important at every cycle to provide energy, form structural components and regulate body functions, according to Judith Brown in "Nutrition Through the Life Cycle." Although basic nutrients such as carbohydrates, protein and fat, vitamins, minerals and fiber are needed throughout life, requirements for energy and nutrients vary in complexity, combination, amounts and proportions to meet physical needs in various life cycles.
Psychosocial
John Santrok, in the text "Life-Span Development," describes Erik Erikson's theory of psychosocial development that features eight stages of human development. Each stage confronts individuals with a crisis that requires overcoming a challenging developmental task. For instance, in the first year of life the development of trust in caregivers becomes necessary because of complete dependency. Infants and toddlers assert their will and growing sense of independence.
Preschoolers and children develop initiative and industry as they focus on mastering knowledge and increasing skills. Adolescents experience a sense of identity, and early adults form intimate relationships with others. In late adulthood, people experience integrity or despair as they evaluate their lives.
Cognitive
According to Santrock in "Life-Span Development," Jean Piaget, a developmental psychologist, believes people go through four age-related stages in understanding the world. In the sensorimotor stage from birth to two years, infants and toddlers understand the world by coordinating what they see, hear, taste, touch and smell with their motor actions such as moving their hands to grasp or putting something in their mouth.
In the preoperational stage children begin to use words, images and symbols. The concrete stage brings logical reasoning to the forefront, and in the formal operational stage people think in abstract and logical terms.
References
- "Nutrition Through the Life Cycle, Third Edition"; Judith E. Brown; 2008
- "Life-Span Development"; John Santrock; 1997
